The present invention relates to a gas/liquid heat exchanger having an upright pressure tank that includes a water chamber, at least one heat-transfer-surface unit, which is disposed in the water chamber and extends along the tank, a saturated steam chamber disposed above the water chamber, and built-in components that divide the water chamber into regions or zones of: water that flows upwardly along the heat-transfer-surface unit, water that flows downwardly, and calm water; each heat-transfer-surface unit includes a displacement body and heat-transfer-surface elements, especially helical heat-transfer-surface elements, that are disposed about the displacement body and have hot process gas under pressure flowing through them.
A heat exchanger of this general type is disclosed in U.S. Pat. No. 4,538,676, which belongs to the assignee of the present application. With this known heat exchanger, the exit temperature of the process gas as it leaves the pressure tank is always about 30.degree.-40.degree. C. greater than the saturated steam temperature. It is not possible to cool the process gas any further, because the temperature difference between the temperature of the steam/water mixture and the exit temperature of the process gas is already very small, and the efficiency of the heat-transfer surfaces is correspondingly low. After leaving the heat exchanger, the process gas is customarily rid of particulates in a wet scrubber, so that the heat content of the process gas supplied to the wet scrubber can no longer be relied upon for energy exploitation.
It is therefore an object of the present invention to provide a gas liquid heat exchanger of the aforementioned general type with which it is possible to make greater utilization of the heat from the process gas; in other words, a heat exchanger that has an improved efficiency.
A further object of the present invention is to reduce the size of the heat-transfer surfaces of the heat exchanger while maintaining the exit temperature of the process gases therefrom.